This invention relates to a stabilized, storable liquid lawn fertilizer. More particularly, it relates to a nitrogen-phosphorous-potassium (N-P-K) fertilizer comprising a methylol urea containing solution and dibasic potassium phosphate, K.sub.2 HPO.sub.4, and the method of using such a fertilizer.
Urea formaldehyde polymers have been used for many years in the preparation of fertilizers. In fact, they find utility in all physical types of fertilizers--solid, suspended solids, and liquid.
Ureaform is a generic name for fertilizer grade urea formaldehyde condensates which were developed to provide controlled release of nitrogen to growing plants. This slow release of nitrogen gives a reduced tendency to burn, as is well known. At first, ureaform fertilizers were solid ones. Numerous patents have issued to various methods for preparing solids ureaform and solid ureaform fertilizer mixtures, including ones in which some form of potassium phosphate is utilized. See, for example, Greidinger, U.S. Pat. No. 4,089,899; Murphy, U.S. Pat. No. 3,479,175; and O'Donnell, U.S. Pat. No. 2,830,036.
Griedinger relates to a solid ureaform compound having a low average degree of polymerization between urea and formaldehyde. It is disclosed that this is accomplished by preparation of the ureaform in a controlled solution medium such as H.sub.3 PO.sub.4 -KH.sub.2 PO.sub.4 and H.sub.3 PO.sub.4 -NH.sub.4 H.sub.2 PO.sub.4. Murphy discloses producing a solid fertilizer having a relatively high nitrogen, phosphorous, and potassium content and which is in the form of dry readily spreadable granules or pellets of uniform composition. Thus, in addition to the urea-formaldehyde resin, the mixture of Murphy contains at least one phosphorous-containing compound selected from the group consisting of monoammonium phosphate, diammonium phosphate, monocalcium phosphate, potassium phosphate and phosphoric acid, and at least one potassium-containing compound selected from the group consisting of potassium chloride, potassium sulfate, potassium nitrate, and potassium phosphate. Finally, O'Donnell produces a solid ureaform fertilizer using a buffer solution which may be a mixture of monopotassium phosphate and dipotassium phosphate.
Still, there are a number of advantages to application of liquid fertilizers. For this reason, some have used an aqueous suspension of solid urea-form fertilizers. One in particular has suggested addition of monopotassium phosphate to a solid fertilizer which may be suspended in this manner.
Thus, Funk in U.S. Pat. Nos. 4,036,627 and 4,089,670 discloses a dry homogeneous blend that may be carried in liquid for application to surface or subsurface areas by conventional liquid fertilizer applying equipment. His mixture is of a low bulk density provided ureaform having soluble and insoluble components combined with soluble monopotassium phosphate. The mixture may be shipped and stored as dry materials and later mixed with water for use.
For the most part, this is an unsatisfactory means to obtain the stability and shipping advantages of a dry material and the application advantages of a liquid one. The suspension is not stable and, therefore, each application amount must be mixed at the time of use. Likewise, mixing equipment may be required to keep the solids uniformly suspended and prevent clogging of hydraulic equipment. Even then, granular or pellet sized particles which will not dissolve in water will not pass through the openings in conventional injection equipment. Care must be taken, as in Funk, to make absolutely sure that the blend of powdered synthetic organic fertilizer material is of a size to pass at least a 60-mesh sieve.
Accordingly, it would be more desirable to use a liquid urea-formaldehyde based fertilizer if certain stability problems could be overcome. Of course, liquid urea-formaldehyde fertilizers in themselves are well known. Waters in U.S. Pat. No. 3,096,168 prepared suspensions of ureaform in liquid mixed fertilizers. These suspensions of urea-formaldehyde resin in water were prepared by reacting 1 to 2.5 moles of urea per mole of formaldehyde under acid conditions. The acid medium is preferably phosphoric acid, to which may be added a potassium compound such as potassium chloride. Later in the process, the phosphoric acid is neutralized with ammonia to form an ammonium phosphate. An improvement on the Waters patent was taken out by Formani in U.S. Pat. No. 3,677,746. The improved process was said to produce a liquid fertilizer suspension containing ureaform having a water insoluble nitrogen content of at least 1.5% and an activity index in excess of 60.
However, as noted in Moore U.S. Pat. No. 4,033,745, neither of the fluid products of Waters and Formani may be stored for commercially required periods of times. Moore attributes this to the fact that the urea-formaldehyde polymers continue to grow in molecular weight and within several days, the fluid fertilizer turns into a semi-solid which cannot be handled in pipes, pumps, nozzles and tanks. Finally, Moore notes that the use of highly diluted products to prevent gelling and solids formation, results in the urea-formaldehyde polymers settling rapidly to the bottom of the storage or distribution tanks.
Moore's solution to this problem is to add alcohol and sugar additives in an effort to stabilize the polymers for storage. It is stated that the alcohol inhibits the growth, gelling, and precipitation of the neutral urea formaldehyde polymers in the fertilizer. The carbonyl groups of the sugars are believed by Moore to react with the urea-formaldehyde polymer, causing thickening and gell formation which stabilizes the suspension and inhibits layer separation and precipitation. The result is a composition stable and storable for 60 or so days.
While this is certainly an improvement on the one-day storability of Waters and Formani, it is still by far too short a period of time in many instances. Obviously, if the liquid fertilizer is to be bottled and sold over the counter, if must be storable for longer than 60 days. Even the large lawn care companies need at least season-long storage capabilities.
Accordingly, the need exists for a stable liquid area formaldehyde type fertilizer which is storable for at least 6-8 months.